Electrolysis of solutions and apparatus thepefor



A. H. HUOKER.

ELECTROLYSIS OF-SOLUT|ONS AND 4APPARATUS THEREFOR.

APPLICATION 'FILED AUG-5, |920.

Patented Aug.l 23, 1921.

Syvum/Ufo@ me,... /J dwf- UNITI-:D STATES i ALBERT H. HOOKER, OF NIAGARA FALLS, NEW YORK, ASSIGNOR T HOOKER ELECTRO- PATENT OFFICE,

CHEMICAL coMrANY, or NEW Yoan, N, Y., A conPoRATicN or NEW vomi.`

mnofraomzsis or SOLUTIONS Application led August 5,

To all whomA it may concern.'

Be it known that ll, ALBERT H. Hooiinn,

a citizen of the United States, residing at paratus and process Niagara Falls, in the county of Niagara and State of New York, have invented certain new and useful Improvements in trolysis of Solutions and Apparatus There, for, of which the following is a specifica tion.

This invention relates to the electrolytic decomposition of solutions, and more particularly to the electrolytic decomposition of sodium chlorid solutions in a cell of the diaphragm type, the primary objects of the invention being to provide an improved apfor the foregoing purposes.

According to the invention in its preerred embodiment the electrolytic cells :receive in unit time a feed of a constant volume of electrol te, for example an aqueous solution. of so ium ehlorid, said electro lyte carryin salt, (typically sodium chlorld) in excess o? the amount normally soluble therein at the operating temperature, this excess of salt being of course present in solid phase at the moment of introduction of the electrolyte into the cell.

In the ractical operation of the' process, the quantity of salt thus supplied in solid phase is nearly but not quite sufficient to maintain the brine within the cell in a con-- dition of complete saturation at the operating temperature: an excess of solid salt above the uantity required lforLQtlier saturation of (tlhe electrolyte v`witliii'iff'jthe cell should however be carefully avoided, as leadin to the. clogging of the diaphragm and ot erwise interfering with the smooth conduct of the operation.

In explanation of the desirability of proceeding in the manner outlined above, it may be explained that it is a well established fact that if unsaturated brine is fed to an electrolytic cell of the diaphragm type at the rate necessary merely to maintain percolation throughthe diaphragm, `with-- out an overflow, the gravit' of the brine within the cell 'falls below t at of the feed brine by a definite amount, which is dependent upon tlie percentage of decomposi tion. For example in a special ease, operating under conditions as above, *he brine within the cell was found to contain on the average 254 grains of salt per liter, although Specification of Letters Patent.

A ND APPARATUS THEBEFOR.

Patented Ailg. 23, 1921. i920. serial Nn. 401,391.

aphragm, so that the operation of the cell soon becomes stabilized: but the specific gravity of the solution within the cell is permanently lowered. This is objectionable as tending not only to a higher operating voltage but to a lower concentration of caustic solutions.

My researches have indicated that thev above described dilution of the brine is a function of the quantity of caustic produced'; and that for every 100 grams of caustic delivered from the 'cell approximately 180 grams of water are left behindA in the cell. If, for example, the feedbrim contains 292.5 grams of sodium chlorid Iper liter and the per cent. of decomposition is 50, this will amount to about 21% of the total water delivered to the cell with the ins flowing brine. If it were possible to discharge this water from the anode side of the cell, the amount of water to be evaporated from the caustic would of course be correspondingly reduced: but the same object may be attained by keeping the concentration of thezliquor within the cell approxrl mately up to that of the feed liquor; or in other wordsas near as practicable at the saturation point.

An obvious method of maintaining the concentration of the brine within thecell is 'to add solid salt to the cell, .and itv has `fraijhuently been proposed to maintain within t e cell a supply ofzsolid salt suiicent for this purpose. According, tc .y my researches however such salt must be added gradually or continuously and in liti'ictly measured uantity; tity is ad ed in unit time, or it be` attempted to vmaintain a permanent supply. Uf solid salt within the cell,'tl1e (lia lragni will rapidly become obstructed and o no' mal operation of the cell will* be actions y affected. Hence, as above Astated "it has I proven impractic'able t0 accomplish' this result by 'maintaining a, supply of solid salt `sprockets 10 and 12.

at all times 1n contact with the electrolyte Within the cell, as has often been proposed.

y researches have shown Ithat only such quantity of salt may be added as will, from a practical or operating viewpoint, pass iinn mediately into solution; and the brine Within the cell should at all times be kept safely below the saturation limit at the operating temperature.

For a full understanding of the invention reference is made to the accompanying drawings illustrating a typical system suit able for carrying the present process into effect, it being however understood that the invention is not restricted to the particular means chosen for illustration.

In said drawings:

Figure 1 is a diagrammatic elevation, partly in. section, of a typical circulating and feeding' system; Fig. 1a being a plan view of the constant level tank 6;

Fig. 2 is a partial vertical section of the same on a slightly enlarged scale on line 2-2 of Fig. 1; and I Figs. 3, 4 and 5 are detail/sectional views of various types of feed nozzles which may be employed.

Referring to Figs. 1, 1 and 2, 2 represents the brine storage tank; 3 the salt hopper containing fine granulated salt such as may be obtained by evaporation of the caustic liquor produced in the operation of the cells; 4 the mixing and agitating tanlr; 5, 5, 5, 5 the electrolytic cells; and G the levelre ulating tank.

he tank i is filled with brine from the tank 2 by opening the valve 7. 8 is a brinemetering device which may be power-driven or may -take the form of a geared rotor pump of the Root blower type, as more clearly illustrated in Fig. 2. The brine flowing through this metering device turns the rotor 9, which drives the sprocket 10, and, through chain 117 the large sprocket 12, the latter revolving a double-Hight worm conveyor 13 which extends throughout the length of the salt hopper at the bottom thereof. This worm feeds the dry salt forward into the vertical open-ended pipe 14e.

The stream of brine from tank 2 is likewise.

directedinto the pipe 14, where it washes the salt out of the worm as fast as it is fed forward,"and carries it through the screen 15 and chute 16 into the mixing and agitan ing tank 4. There is therefore in the operation of this device, a fixed relation between the displacement of the brine-meter and the salt feed so that a definite and controllable quantity of salt can be fed v.for a given quantity of brine. The feed ratios may be adjusted as desired by a proper choice of Itffwillbe understood that the tank 2 might be filled with Water or weak brine, and'V by feeding the proper quantity of-solid recente salt a saturated, under-saturated or oversaturated brine can be delivered into tank d at will. For the purpose of the present invention, however, a brine carrying an excess of salt in solid phase will be required; and it 'is generally preferable to obtain this by filling the' tank 2 with brine having a specic gravity in the neighborhood of 1. 2, and adding through the hopper 3 the salt necessary to provide the required excess.

In the system chosen for illustration the tank et is provided 4with a centrifugal pump 17 driven by a motor 18. The intake 19 of the pump 17 is located close to the bottom of the tank d, and agitators 2O are mounted upon the vertical pump shaft. The delivery pipe 2l 'from pump 17 carried over the cells 5 and. terminates in an elbow 22, lom cated within the level-regulating bank 6 and directed tangentially near the bottoni there of (sec Fig. F). 23 is the overiiow inlet leading to the return pipe 2e', terminating in an elbow 25 which may be directed tann gentially near the bottom of tank 4.

By means of the pump 17 and the pipes 21 and 2li a rapid circulation of the salt susn pension is maintained. "lhherebj7 the mixture in the tank e is kept in violent agita tion and the undissolved salt is maintained in suspension during its dow to the tank 6 and return= 26 indicates a screen which may be placed across the tank 6 between. the inflow and outflow to trap any foreign mat ter which may find its way into the system. A 20-mesh screen has proven satisfactory for this purpose, being suiciently coarse to permit free passage of the tine solid salt, while sufficiently line to remove any foreign matter that would be liable to interfere with the feed o" the brine tothe cells er with the operation of the latter.

lAbove each. cell 5 is provided a feeding orifice or nozzle 2'?. A simple form of such orifice is illustrated on an eniarged scale in Fig. 3, comprising a calibrated glass tube 28 let into the pipe 21 through a rubber stopper by means of a tee 29. The stream of brine from the tube 28 is directed into a glass tee 30, which discharges in turn into the cells, for example through lengths of rubber hose 31, connected with earthen ware well-pipes 32, which extend to a point well below the liquid level. Naturally any preferred device may be used for conveying the salt suspension to the cells or distributing it therein.

^ The hydrostatic head upon the orice 27 is determined by the level of the liquid in the tank 6. This may be adjusted as desired by changing the edective height .of the overflow pipe 23, which can conveniently be done by screwing diferent lengths into the cou` p ing 33. .oo long as the level in the tank 6 1s maintained constanhthe orifice 28 will feed a constant quantity of brine in unit therein.

Fig. 4 yillustrates a stream-line type of orifice, screwed flush into the pipe 21 and terminating in a succession vof tapered nozzles 34, screwed one upon the other,'each successive nozzle being slightly smaller than the preceding one with the result that toether they form a uniformly tapering orice of which the aperture may be closely regulated.

The types of orifice illustrated in Figs. 3 and 4 are not aifected by tlie velocity of the flow in pipe 21, except as the resistance to such liow creates added static pressure. Thus, it' the pipe 21 be horizontal, the ori- '.(ice leading to the cell farthest from the tank 6 will be under a higher static pressure than that of the cell nearest this tank, by the amount of the pressure necessary to over come the resistance offered by the walls or f .the pipe 21 to the iow of the salt suspension therein. In order to equalize the static head on' the several orifices, and thereby to equalize the ilow through these orices, the pipe 21 is preferabl inclined toward the regulating tank 6 as i lustrated in Fig. 1. It is very easy to determine experimentally the degree of inclination necessary by connecting a manometer to each orifice, theproper inclination being obtained when all of the manometers give identical readings.l

Fig. 5 illustrates a form of orifice having a curved inlet 35 extending into the interior of the pipe 21. This type of orifice may be adjusted by turning it so as to present various angles to the direction of flow Within the pipe, and is `very sensitive to iuctuations 1n the velocity of the brine.

It is to be noted that by operating in accordance with the present invention I am able not only to feed to the several electrolytic cells a brine carrying solid salt in sus-y pension, but to feed a constant quantity of this suspension in unit time. By applying this method to a diaphragm cell having' no overiow or equivalent constant-level device, I secure an accurate and Wholly automatic control of the percolation through the diaphragm, since the level of electrolyte Within the cell will automatically vary in the direction and to`the precise degree necessary to secure an average percolation equivalent to the infiow. Thereby I am able to insure a constant percentage of decomposition and a constant and high ampere efficiency; While the .maintenance of the saturation of the electrolyte leads to a relatively high emergency eiiiciency. This result in the particu' lar system chosen for illustration is cteendent upon the maintenance of a constant evel in the y 1essureregulating tank 6; but it will be olivious to those skilled in this art that other means may be employed for accomplishing the same result.

The circulating system described herein as a preferred means of securing uniform feed to the electrolytic cells is claimed in a coending application Serial Number 403,326 liled Aug. 13, 1920, by Thomas L. B. Lyster and Kenneth E. Stuart.

l. In a process of electrolyzing salt solutions, the step Which consists in supplying to the cell an aqueous electrolyte carrying a salt in solid phase. E

2. Process according to claim. 1 in which 'the quantity oi salt introduced in unit time is proportioned to maintain approximate satrratien of the electrolyte within the cell.

The combination with an electrolytic cell,v of means for supplying thereto in unit time a fixed volume of electrolyte carrying salt in solid phase.

In testimony lwhereof, I aiiix my signature.

ALBERT H. HOOKER. 

